Hydraulically actuated latches are used on some rocker arm assemblies to implement variable valve lift (VVL) or cylinder deactivation (CDA). For example, some switching roller finger followers (SRFF) use hydraulically actuated latches. In these systems, pressurized oil from an oil pump may be used for latch actuation. The flow of pressurized oil may be regulated by an oil control valve (OCV) under the supervision of an engine control unit (ECU). A separate feed from the same source provides oil for hydraulic lash adjustment. In these systems each rocker arm assembly has two hydraulic feeds, which entails a degree of complexity and equipment cost. The oil demands of these hydraulic feeds may approach the limits of existing supply systems.
The complexity and demands for oil in some valvetrain systems can be reduced by replacing hydraulically latched rocker arm assemblies with electrically latched rocker arm assemblies. Electrically latched rocker arm assemblies require power. Regardless of whether electric latches are used, there has been a long felt need to provide sensors on switching and cylinder deactivating rocker arm assemblies to provide diagnostic information.